Modified melamine resins and their use for producing postformable laminates

ABSTRACT

Modified melamine-formaldehyde resins are made of a condensate of formaldehyde, urea, melamine and modifying agents which contains: (a) a combination of 5 to 25 wt %, with respect to melamine, of dicyanodiamide and 8 to 30 wt %, with respect to melamine, of water-soluble polyalcohol with at least two hydroxyalkyl groups, and/or (b) 1.5 to 20 wt % amines having the formulas (Ia) 
     
         NR.sub.4 R.sub.5 --R.sub.1 --X                             (Ia) 
    
     and/or (Ib), 
     
         NR.sub.4 R.sub.5 --R.sub.2 --Y--R.sub.3 --X                (Ib) 
    
     in which R 1  and R 3  are the same or different and depending on the meaning of X stand for a linear, branched or cyclic C 1  -C 12  alkyl or alkylene radical and R 2  stands for a linear, branched or cyclic C 1  -C 12  alkylene radical; R 4  and R 5  can be the same or different and can stand for H or for a linear or branched C 1  -C 12  alkyl radical; and X can stand for hydrogen, OH or NR 4  R 5  and Y can stand for --O-- or --NH--. The molar ratio of melamine to formaldehyde ranges from 1:1.2 to 1:5 and the molar ratio of melamine to urea ranges from 1:0.1 to 1:2.8. Also disclosed is the use of these resins to produce post-forming laminates.

Melamine resin laminates based on impregnated papers have a wide fieldof use as decorative and protective surfaces because of their goodfastness to light, abrasion resistance, resistance to chemicals,resistance to glowing heat and surface hardness.

Such laminates which are obtained by impregnation of carrier webs oftextiles, paper or glass nonwovens with aqueous solutions ofmelamine-formaldehyde precondensates and subsequent drying and curing attemperatures above 100° C. are described, for example, in EP-A-0 077067. EP-B1-0 268 809 describes melamine resin films which are obtainedby coating papers with an at least 70% strength by weight aqueoussolution of a melamine resin etherified by methyl.

The disadvantage of these known melamine resins and melamine resinlaminates is, in particular, that they show a relatively high shrinkageduring curing, that their mechanical properties, such as, for example,resistance to boiling water, are inadequate in many cases, and thatabove all they are very brittle and show no postforming properties.

It is known from U.S. Pat. No. 4,424,261 that the use ofhydroxyalkylmelamines as modifying agents for melamine-formaldehyderesins leads to an improvement in the postforming properties. However,the disadvantage of these modifying agents is their instability, whichmeans they are not easily available and furthermore can be handled onlywith difficulty, since they have a marked tendency to undergoself-crosslinking.

Other modifying agents, such as, for example, guanamines, which lead topostforming properties of the resins, are described in EP-A1-0 561 432.However, guanamines, especially those with aromatic nuclei, such asbenzoguanamine, do not have an adequate resistance to light, which meansthat the modified resins yellow easily. Furthermore, the low solubilityof the guanamines in the reaction medium has an adverse effect on thepreparation process for the resins.

WO-A-9620 230 furthermore discloses resins consisting of the componentsformaldehyde melamine, dicyandiamide in an amount of 5 to 25% by weightbased on the melamine and a polyalcohol such as trimethylolpropane in anamount of 8 to 30% by weight based on the melamine. Although theseresins also show postforming properties and resistance to boiling water,the possibility of converting these resins into powder form by spraydrying is not described.

EP-A-0 007 705 discloses resins which comprise melamine, formaldehydeand a hydroxymonoamine, part of the melamine being replaced by urea.Properties such as postforming, resistance to boiling water andsuitability for spray drying are not described.

It was therefore necessary to discover a modifying agent for melamineresins which does not have the disadvantages of the modifying agentsknown to date and greatly improves the postforming properties of themelamine resins without reducing their resistance to boiling water andwhich leads to resins which can-be spray-dried. It has now been found,unexpectedly, that such melamine resins are obtained by using specialmodifying agents comprising a combination of certain polyalcohols anddicyandiamide or certain amines, and addition of urea.

The present invention accordingly relates to modifiedmelamine-formaldehyde resins which comprise a condensate offormaldehyde, melamine, urea and modifying agent comprising

a) a combination of 5 to 25% by weight, based on the melamine, ofdicyandiamide and 8 to 30% by weight, based on the melamine, ofpolyalcohol of the formula

    R.sub.1 --(R.sub.2 OH).sub.3                               Ia

or

    HOR.sub.4 --R.sub.3 --R.sub.5 OH                           Ib

in which, in the formula Ia, R₁ is a radical of the formula ##STR1##where n is 0 to 3, IIa or a radical of the formula ##STR2## R₂ is alinear or branched (C₁ to C₄)alkylene radical and, in the formula Ib, R₃is a cycloalkylene radical having 6 C atoms or R₃, like R₄ and R₅ is alinear or branched (C₁ to C₆)alkylene radical, which can optionally besubstituted by a further hydroxyl group, where R₃, R₄ and R₅ can beidentical or different and/or

b) amines of the formulae

    NR.sub.4 R.sub.5 --R.sub.1 --X                             IIIa

and/or

    NR.sub.4 R.sub.5 --R.sub.2 --Y--R.sub.3 --X                IIIb

in which R₁ and R₃ can be identical or different and, depending on themeaning of X, are a linear or branched or cyclic C₁ to C₁₂ -alkyl oralkylene radical and R₂ is a linear or branched or cyclic C₁ to C₁₂-alkylene radical, R₄ and R₅ can be identical or different and are H ora linear or branched C₁ to C₁₂ -alkyl radical, and X can be hydrogen, OHor NR₄ R₅ and Y can be --O-- or --NH--,

the molar ratio of melamine to formaldehyde being 1:1.2 to 1:5 and thatof melamine to urea being 1:0.1 to 1:2.8.

The melamine resins according to the invention are thus modified by acombination of dicyandiamide with polyalcohols, of the formula Ia or Ib,or by the specific amines of the formulae IIIa and/or IIIb.

Polyalcohols, of the formula Ia or Ib contain at least two hydroxyalkylgroups, and here are compounds in which the hydroxyalkyl groups arebonded to an aliphatic, cycloaliphatic or heterocyclic core structure.Aliphatic core structures are to be understood here as meaning linear orbranched C₁ to C₁₀ alkylene groups, which can optionally be substitutedby carbonyl, amino or (C₁ -C₆)-alkoxy groups. Possible cycloaliphaticcore structures are C₅ to C₈ cycloalkylene groups, which can likewiseoptionally contain further substituents such as, for example, carbonylgroups, in addition to the hydroxyalkyl groups. The heterocylic corestructure can contain 1 to 3 hetero atoms, such as N, O or S, in thering, and optionally further substituents, such as, for example,carbonyl radicals. The alkyl part of the hydroxyalkyl groups here has 1to 6 C atoms.

Preferred polyalcohols are those of the formula

    R.sub.1 --(R.sub.2 OH).sub.3                               Ia

or

    HOR.sub.4 --R.sub.3 --R.sub.5 OH                           Ib

in which, in the formula IIa [sic] a radical of the formula ##STR3##where n is 0 to 3, is R₁ or a radical of the formula ##STR4## R₂ is alinear or branched (C₁ to C₄)-alkylene radical.

In the formula Ib), R₃, R₄ and R₅ are a linear or branched (C₁ toC₆)-alkylene radical, which can optionally be substituted by a furtherhydroxyl group. R₃, R₄ and R₅ here can be identical or different. R₃ canfurthermore also be a cycloalkylene radical having 6 C atoms.

Particularly preferred polyalcohols here are trimethylolpropane,trimethylolethane, trishydroxyethyl isocyanurate, neopentylglycol,1,4-dimethylolcyclohexane, 4-methyl-2,4-pentanediol, 1,6-hexanediol,3-methyl-1,3,5-pentanetriol and 2,2,4-trimethyl-1,3-pentanediol.

The polyalcohols can be added both as an individual compound and as amixture of several polyalcohols. The amount of polyalcohol in themelamine resin according to the invention is about 8 to 30% by weight,based on the melamine employed. About 12 to 22% by weight ofpolyalcohols is preferably employed.

According to the invention, the polyalcohols are used in combinationwith dicyandiamide as modifying agents for melamine-formaldehyde resins.The amount of dicyandiamide here is about 5 to 25% by weight, based onthe melamine employed, preferably about 8 to 18% by weight.

The melamine resins according to the invention can also be modified byamines of the formulae IIIa and/or IIIb, instead of the combinationdescribed above.

In the formulae IIIa and IIIb, R₁ and R₃ are, depending on the meaningof X, a C₁ to C₁₂ -alkyl or alkylene radical, which can be linear,branched or cyclic. Examples of these are methyl, ethyl, n-propyl,i-propyl, n-butyl, sec-butyl, tert-butyl, hexyl, decyl, dodecyl,methylene, ethylene, n-propylene, i-propylene, n-butylene, sec-butylene,tert-butylene, hexylene, decylene, dodecylene, cyclohexyl or cyclodecyl.Cyclic radicals here can be optionally substituted by further alkylgroups. Linear, branched or cyclic C₁ to C₆ -alkyl or alkylene radicalsare preferred.

R₂ in the formula Ib is a linear, branched or cyclic C₁ -C₁₂ -alkyleneradical as defined above. Linear, branched or cyclic C₁ -C₆ -alkyleneradicals are preferred. R₄ and R₅ in the formulae Ia and Ib can beidentical or different and are H or a linear or branched C₁ -C₁₂ -alkylradical as defined above. R₄ and R₅ are preferably hydrogen.

X in the formulae IIIa and IIIb can be hydrogen or a hydroxyl or anamine radical. Amine radicals here are to be understood as meaning bothprimary, secondary and also tertiary amine radicals of the formula --NR₄R₅, in which R₄ and R₅ are as defined above.

Y in the formula Ib [sic] is --O-- or --NH--.

Examples of amines of the formulae Ia and Ib [sic] are ethylamine,butylamine, hexylamine, methoxypropylamine, ethoxypropylamine,diglycolamine, ethylenediamine, propylenediamine, hexylenediamine orisophoronediamine. Amines such as, for example, ethoxypropylamine,diglycolamine or isophoronediamine are preferred.

The amines of the formulae IIIa and IIIb can be used both as anindividual compound and as a mixture of several amines. The amount ofamine in the melamine-formaldehyde resin according to the invention isabout 1.5 to 20% by weight, based on the melamine. About 2.5 to 15% byweight of amine is preferably employed.

If appropriate, a mixture of the modifying agents a) and b) can also beemployed.

However, the combination of polyalcohol and dicyandiamide is preferablyemployed as the modifying agent.

The molar ratio of melamine to formaldehdye in the resins to be modifedis 1:1.2 to 1:5. Melamine and formaldehyde are preferably employed in amolar ratio of 1:1.4 to 1:2.8.

Urea is furthermore cocondensed in the resins according to theinvention. The molar ratio of melamine to urea here is 1:0.1 to 1:2.8,preferably between 1:0.15 and 1:1.

The melamine-formaldehyde resins modified according to the invention areobtained by subjecting melamine and urea to a condensation reaction withformaldehyde in a known manner in aqueous solution and admixing themodifying agent in the abovementioned amount before or during thecondensation. If combination a) is used, the polyalcohol anddicyandiamide components can be added here both as a mixture and asindividual components. For preparation of the resins according to theinvention, however, it is also possible to employ a finished mixturecomprising melamine, urea, formaldehyde and amine and/or dicyandiamideand polyalcohol.

The present invention furthermore accordingly relates to the use of amixture of formaldehyde, urea, melamine and

a) 5 to 25% by weight, based on the melamine, of dicyandiamide and 8 to30% by weight, based on the melamine, of polyalcohol of the formula

    R.sub.1 --(R.sub.2 OH).sub.3                               Ia

or

    HOR.sub.4 --R.sub.3 --R.sub.5 OH                           Ib

in which, in the formula Ia, R₁ is a radical of the formula ##STR5##where n is 0 to 3, IIa or a radical of the formula ##STR6## and R₂ is alinear or branched (C₁ to C₄)alkylene radical and, in the formula Ib, R₃is a cycloalkylene radical having 6 C atoms or R₃, like R₄ and R₅ is alinear or branched (C₁ to C₆)alkylene radical, which can optionally besubstituted by a further hydroxyl group, where R₃, R₄ and R₅ can beidentical or different or

b) 1.5 to 20% by weight, based on the melamine, of amines of the formulaIIIa and or [sic] IIIb, which comprises melamine and formaldehyde in amolar ratio of 1:1.2 to 1:5 and melamine and urea in a molar ratio of1:0.1 to 1:2.8, for the preparation of modified melamine-formaldehyderesins.

However, a highly modified melamine-formaldehyde resins [sic] can alsobe prepared in a preliminary stage by addition of 40 to 60% by weight ofamine, based on the melamine. This highly modified melamine-formaldehyderesins [sic] can then be employed as a modifying agent for thepreparation of the melamine-formaldehyde resin (MF resin) according tothe invention. The weight ratio of modifying agent to MF resin here is1:2 to 1:6, preferably 1:3.

The present invention furthermore accordingly relates to the use of amelamine-formaldehyde resin which comprises 40 to 60% by weight of amineof the formula IIIa and/or IIIb, based on the melamine, and melamine andformaldehyde in a molar ratio of 1:1.2 to 1:5 and melamine and urea in amolar ratio of 1:0.1 to 1:2.8, for the preparation of modifiedmelamine-formaldehyde resins.

To accelerate the reaction in the modification of the melamine resinswith the combination according to the invention, customary catalysts,such as, for example, p-toluenesulfonic acid, can be added in amounts ofabout 0.1 to 1% by weight, based on the total amount of the melamineresin.

Hydrolyzable salts of weak to strong carboxylic acids, sulfonic acids ormineral acids, for example diethanolamine acetate, morpholine,diethanolamine, ethanolamine hydrochloride, ethylenediamine acetate,ammonium thiocyanate, ammonium lactate, ethylenediamine phosphate or thedimethylethanolamine salt of p-toluenesulfonic acid, can furthermorealso be added to the resins in order to accelerate the curing, withoutthe elasticity of the resins being impaired as a result.

If appropriate, additional modifying agents, such as ε-caprolactam oraromatic sulfonic acid amides, such as p-toluenesulfonamides, can alsobe added during the preparation of the resins in an amount of 0 to 40%by weight, preferably 0-20% by weight, based on the melamine.

The condensation of the resins is as a rule continued up to a limitedwater-dilutability.

If desired, the resins thus prepared and the highly modified resins usedas modifying agents can be converted into powder form by spray drying.The resins are preferably dried here to a residual moisture content of1-1.5%, for example by means a centrifugal or an air drier. The resinsdried in this way must then be disolved in water before their use.

On the basis of their outstanding properties, such as absence of phenoland therefore environment-friendliness, and no waste gas problems duringthe impregnation, the melamine-formaldehyde resins modified according tothe invention are suitable for a large number of uses.

The melamine-formaldehyde resins modified according to the invention areparticularly suitable for the production of decorative or protectivesurfaces having excellent postforming properties. The precursors (films)of the decorative or protective surfaces are produced by impregnation ofwebs of paper or fabric. Paper webs are preferably made of decorativepaper or kraft paper. Fabric webs here preferably comprise a nonwoven,woven fabric or fiberwoven fabric of glass, carbon, ceramic or aramidfibers. Depending on the requirements regarding the properties of thelaminates thus produced, mixtures of different fibers, unidirectionalcontinuous fibers or several layers of the same or different reinforcingwebs can also be employed.

The impregnation of these webs with the melamine-formaldehyde resinsmodified according to the invention is carried out, for example, bydipping or spraying and subsequent squeezing off or knife-coating togive the desired resin content of the films. The resin content dependsabove all on the properties required for the films or the laminates andon the nature of the fiber reinforcement, and is usually 30 to 60% byweight, based on the carrier material impregnated with resin.

The impregnation is usually carried out at temperatures of about 20 to60° C., depending on the viscosity and consistency of the melamineresin. To obtain a film which can be stored, the films are dried atabout 80 to 160° C. to a particular residual moisture content after theimpregnation, the readily liquid impregnating resin reacting more orless with partial curing and crosslinking, depending on the temperatureand the duration of the heat treatment.

In this state, the film can be stored and transported at about roomtemperature. Several layers of impregnated kraft and decorative papersare then pressed at a temperature of 120 to 180° C. under a pressure of25 to 100 bar to give the laminate. On the basis of the excellentpostforming properties, the laminate can be shaped to the desiredmolding at temperatures of 80 to 180° C. under pressure, with furthercrosslinking of the melamine resin.

The laminates obtained from the resins modified according to theinvention are distinguished above all by a high resistance to boilingwater, and by an improved elasticity of their surface, so that lowbending radii can be achieved with cracking being avoided.

EXAMPLE 1

126 parts (1 mol) of melamine, 146.7 parts (1.76 mol) of 36% strengthformaldehyde solution, 20 parts (0.15 mol) of trimethylolpropane, 14.7parts (0.175 mol) of dicyandiamide, 3.6 parts (0.032 mol) ofcaprolactam, 10 parts (0.17 mol) of urea and 70.6 parts of deionizedwater were subjected to a condensation reaction, in a tank with astirrer and reflux condenser, at 90° C. and a pH of 9.3-10 (maintainedwith sodium hydroxide) until a water-dilutability of about 1.2 at 20° C.(1.0 part by volume of resin: 1.2 parts by volume of H₂ O) was reached.

EXAMPLE 2

Analogously to Example 1, 126 parts of melamine (1 mol), 111 parts ofFormurea 80 (concentrated aqueous solution of formaldehyde (2.11 mol)and urea (0.426 mol) produced by Agrolinz Melamin Italia), 21.4 parts(0.16 mol) of trimethylolpropane, 15.9 parts (0.19 mol) ofdicyandiamide, 4 parts (0.035 mol) of caprolactam and 163.2 parts ofdeionized water were subjected to a condensation reaction.

EXAMPLE 3-5

Further modified resins were prepared analogously to Example 1. Theproportion of melamine was in each case 126 parts.

The proportion of formaldehyde (FA), urea (U), H₂ O and modifying agentand the nature thereof can be seen from Table 1.

                  TABLE 1                                                         ______________________________________                                        Ex-   FA      U      DCDA  TMP   CL    DGA   H.sub.2 O                        ample (mol)   (mol)  (mol) (mol) (mol) (mol) parts                            ______________________________________                                        3     2.35    0.64   0.20  0.17  0.036 --    176.6                            4     2.56    0.87   0.11  0.08  --    0.064 175.8                            5     3.72    1.73   0.16  0.10  --    0.093 234.3                            ______________________________________                                         DCDA Dicyandiamide                                                            TMP Trimethylolpropane                                                        CL Caprolactam                                                                DGA Diglycolamine                                                        

EXAMPLE 6

The resins from Example 1 to 5, were catalyzed with 0.2% by weight ofhardener EC15 (Agrolinz Melamin Italia) for 20 minutes to a cloud pointof 100° C. Decorative paper and kraft paper, which functioned as corepaper, were then impregnated. The decorative paper (95 g/m²) comprised aresin proportion of 55% by weight and 6% by weight of volatileconstituents (based on the impregnated paper), and the core paper (80g/m²) comprised a resin proportion of 47% by weight and also 6% byweight of volatile constituents (based on the impregnated paper) A layerof impregnated decorative paper and 5 layers of core paper were thenpressed together under a pressure of 70 bar at 175° C. for 20 seconds.

The laminates thus obtained were investigated for their postformingproperties and their resistance to boiling water. The results can beseen from Table 2.

                  TABLE 2                                                         ______________________________________                                                        Resistance to boiling water                                           Postforming                                                                             Bubble                                                              properties                                                                              formation  Water                                                    Diameter in                                                                             after 2 and                                                                              absorption %                                             mm (*)    6 hours    3S EN 438-2                                      ______________________________________                                        Example 1 <3          no bubbles 10.6                                         Example 2 <3          a few small                                                                              12.1                                                               bubbles                                                 Example 3 <3          a few small                                                                              10.6                                                               bubbles                                                 Example 4 <3          no bubbles  9.4                                         Example 5 <3          a few small                                                                              13.1                                                               bubbles                                                 ______________________________________                                         (*) Smallest diameter around which the laminate specimen (145 × 35      mm) heated to 160° C. can be bent around a metal cylinder by           90° without tearing.                                              

What is claimed is:
 1. A modified melamine-formaldhyde resin whichcomprises a condensate of formaldehyde, melamine, urea and modifyingagent comprisinga) a combination of 5 to 25% by weight, based on themelamine, of dicyandiamide and 8 to 30% by weight, based on themelamine, of polyalcohol of the formula

    R.sub.1 --(R.sub.2 OH).sub.3                               Ia

or

    HOR.sub.4 --R.sub.3 --R.sub.5 OH                           Ib

in which, in the formula Ia, R₁ is a radical of the formula ##STR7##where n is 0 to 3, IIa or a radical of the formula ##STR8## and R₂ is alinear or branched (C₁ to C₄)alkylene radical and, in the formula Ib, R₃is a cycloalkylene radical having 6 C atoms or R₃, like R₄ and R₅ is alinear or branched (C₁ to C₆)alkylene radical, which can optionally besubstituted by a further hydroxyl group, where R₃, R₄ and R₅ can beidentical or different and/or b) 1.5 to 20% by weight of amines of theformulae

    NR.sub.4 R.sub.5 --R.sub.1 --X                             IIIa

and/or

    NR.sub.4 R.sub.5 --R.sub.2 --Y--R.sub.3 --X                IIIb

in which R₁ and R₃ can be identical or different and, depending on themeaning of X, are a linear or branched or cyclic C₁ to C₁₂ -alkyl oralkylene radical and R₂ is a linear or branched or cyclic C₁ to C₁₂-alkylene radical, R₄ and R₅ can be identical or different and are H ora linear or branched C₁ to C₁₂ -alkyl radical, and X can be hydrogen, OHor NR₄ R₅ and Y can be --O-- or --NH--, the molar ratio of melamine toformaldehyde being 1:1.2 to 1:5 and that of melamine to urea being 1:0.1to 1:2.8.
 2. The modified melamine-formaldehyde resin as claimed inclaim 1, wherein the modifying agent comprises a combination ofdicyandiamide and polyalcohol of the formula Ia or Ib.
 3. The modifiedmelamine-formaldehyde resin as claimed in claim 1, wherein thepolyalcohol employed is trimethylolpropane, trimethylolethane,trishydroxyethyl isocyanurate, neopentylglycol,1,4-dimethylolcyclohexane, 4-methyl-2,4-pentanediol, 1,6-hexanediol,3-methyl-1,3,5-pentanetriol or 2,2,4-trimethyl-1,3-pentanediol or amixture thereof.
 4. The modified melamine-formaldehyde resin as claimedin claim 1, which comprises melamine and formaldehyde in a molar ratioof 1:1.4 to 1:2.8 and melamine and urea in a molar ratio of 1:0.15 to1:1.
 5. The modified melamine-formaldehyde resin as claimed in claim 1,which is present in liquid or spray-dried in powder form.
 6. A melamineresin laminate, which comprises webs of paper or fabric impregnated witha modified melamine resin as claimed in claim
 1. 7. A process for theproduction of a melamine resin laminate which comprises impregnating aweb of paper or fabric with a modified melamine resin as claimed inclaim 1, pressing the films obtained during the impregnation to give alaminate, optionally partly curing the laminate, and postforming and asa result completely curing it.
 8. A method for the preparation of amodified melamine-formaldehyde resin, which comprises melamine andformaldehyde in a molar ratio of 1:1.2 to 1:5 and melamine and urea in amolar ratio of 1:0.1 to 1:2.8, comprising mixing formaldehyde, urea,melamine and a) 5 to 25% by weight, based on the melamine, ofdicyandiamide and 8 to 30% by weight, based on the melamine, ofpolyalcohol of the formula

    R.sub.1 --(R.sub.2 OH).sub.3                               Ia

or

    HOR.sub.4 --R.sub.3 --R.sub.5 OH                           Ib

in which, in the formula Ia, R₁ is a radical of the formula ##STR9##where n is 0 to 3, or a radical of the formula ##STR10## and R₂ is alinear or branched (C₁ to C₄) alkylene radical and, in the formula Ib,R₃ is a cycloalkylene radical having 6 C atoms or R₃, like R₄ and R₅ isa linear or branched (C₁ to C₆) alkylene radical, which can optionallybe substituted by a further hydroxyl group, where R₃, R₄ and R₅ can beidentical or different or b) 1.5 to 20% by weight, based on themelamine, of amines of the formula

    NR.sub.4 R.sub.5 --R.sub.1 --X                             IIIa

and/or

    NR.sub.4 R.sub.5 --R.sub.2 --Y--R.sub.3 --X                IIIb

in which R₁ and R₃ can be identical or different and, depending on themeaning of X, are a linear or branched or cyclic C₁ to C₁₂ -alkyl oralkylene radical and R₂ is a linear or branched or cyclic C₁ to C₁₂-alkylene radical, R₄ and R₅ can be identical or different and are H ora linear or branched C₁ to C₁₂ -alkyl radical, and X can be hydrogen, OHor NR₄ R₅, and Y can be --O-- or --NH--,and subjecting the mixture to acondensation reaction.
 9. A method for the preparation of a modifiedmelamine-formaldehyde resin, which comprises melamine and formaldehydein a molar ratio of 1:1.2 to 1:5 and melamine and urea in a molar ratioof 1:0.2 to 1:2.8, comprising mixing formaldehyde, urea, melamine and 40to 60% by weight, based on the melamine, of amine of the formula

    NR.sub.4 R.sub.5 --R.sub.1 --X                             IIIa

and/or

    NR.sub.4 R.sub.5 --R.sub.2 --Y--R.sub.3 --X                IIIb

in which R₁ and R₃ can be identical or different and, depending on themeaning of X, are a linear or branched or cyclic C₁ to C₁₂ -alkyl oralkylene radical and R₂ is a linear or branched or cyclic C₁ to C₁₂-alkylene radical, R₄ and R₅ can be identical or different and are H ora linear or branched C₁ to C₁₂ -alkyl radical, and X can be hydrogen, OHor NR₄ R₅, and Y can be --O-- or --NH--, and subjecting the mixture to acondensation reaction.
 10. A modified melamine-formaldehyde resin whichcomprises a condensate of formaldehyde, melamine, urea and modifyingagent comprising 40 to 60% by weight, based on the melamine, of aminesof the formulae

    NR.sub.4 R.sub.5 --R.sub.1 --X                             IIIa

and/or

    NR.sub.4 R.sub.5 --R.sub.2 --Y--R.sub.3 --X                IIIb

in which R₁ and R₃ can be identical or different and, depending on themeaning of X, are a linear or branched or cyclic C₁ to C₁₂ -alkyl oralkylene radical and R₂ is a linear or branched or cyclic C₁ to C₁₂-alkylene radical, R₄ and R₅ can be identical or different and are H ora linear or branched C₁ to C₁₂ -alkyl radical, and X can be hydrogen, OHor NR₄ R₅ and Y can be --O-- or --NH--, the molar ratio of melamine toformaldehyde being 1:1.2 to 1:5 and that of melamine to urea being 1:0.1to 1:2.8.